I. Field of the Invention
The present invention relates to a production method and system for granulating powdered material, and more particularly relates to a production method and system for efficiently granulating powdered material with uniform property and small specific volume using pulsating vibration air.
II. Prior Art
FIG. 12 shows a known fluidized layer granulation system.
The granulation system 101 is comprised of a granulation tank 102, an air source 103, such as a blower fan, a discharge fan 104, heating means 105, such as a heat exchanger, and spray means 106 such as a nozzle means, for spraying a binding solution.
A supply port 102a for introducing heated air is provided under the granulation tank 102, the air source 103 is connected to the supply port 102a via a conduit pipe and the heating means 105 is provided between the supply port 102a and the air source 103. When the air source 103 is driven to cause the heating means 105 also to drive, the air produced by the air source 103 is heated by the heating means 105, the heated air is supplied into the granulation tank 102 from the supply port 102a, and the supplied air is blown up in the granulation tank.
A fluidization bed 107 is provided above the supply port 102a in the granulation tank 102. Powdered material A stored in the granulation tank 102 is deposited on the fluidization bed 107 when air isn""t supplied to the granulation tank 102.
Whereas heated air is supplied from the supply port 102a, the powdered material A deposited on the fluidization bed 107 floats to be mixed with the air blown upward from the fluidization bed 107 and forms a fluidized layer following the increase of the wind speed of the supplied air.
Further, a discharge port 102b is provided on the top of the granulation tank 102 and the discharge fan 104 is connected to the port 102b via a conduit pipe. The air supplied to the granulation tank 102 is discharged to the outside by driving the fan 104.
On the other hand, the spray means 106 for spraying a binding solution is provided in the granulation tank 102 and connected with an air source 108 storing pressurized air via an air supply pipe 109, and further a tank 110 for storing a binding solution is connected via a binding solution supply pipe 111. A control unit 112 for adjusting the spraying amount of the spray means 106 is interposed in the middle of the pipe 111.
In FIG. 12, the numeral 113 relates to a bag filter for preventing the raw powdered material A, the granulating material or the granulated material from flowing out of the granulation tank 102 and the numeral 114 relates to a dust collecting filter for eliminating dust in the air supplied to the granulation tank 102.
In order to granulate material utilizing the system 101, the raw material A is stored in the granulation tank 102. Heated air is supplied into the tank 102 by driving the air source 103 and the heating means 105 and simultaneously the discharge fan 104 is driven, whereby the raw material A placed on the fluidization bed 107 is caused to be blown up. The heated air with constant flow amount and constant pressure is always supplied into the tank 102 by controlling the driving force of the air source 103 and the discharge fan 104 so that a desired stable fluidized layer is formed in the tank 102. Thereafter, air with a fixed pressure is supplied to the spray means 106 for spraying a binding solution from the air source 108 and simultaneously the control unit 112 is driven. A binding solution B is sprayed from a desired spray and makes a bridge of solution between particles of the raw material A. The particles of the raw material A suspended in the granulation tank 102 as a fluidized layer mixed with air are aggregated and the aggregated particles are dried to be grown as a granulated material.
In the prior granulation method mentioned above, the granulated material with uniform physical properties (particle diameter, particle shape, etc) can be produced when material is granulated by spraying a binding solution from the nozzle after a dilute fluidized layer is formed by supplying a large amount of heated air with constant pressure and constant amount into the granulation tank 102.
It is known that an increased speed of the particles becomes fast when particles are granulated by spraying a binding solution from the nozzle after a high density fluidized layer is formed by reducing the amount of heated air supplied into the granulation tank 102.
However, when material is granulated by means of the system 101, the granulated material becomes porous and its specific volume increases and becomes large because it is made from the particles floating in the air. In order to solve this problem, a new granulation method has been proposed in JP-A-60-183030.
FIG. 13 is a partially cutaway sectional view of the system disclosed in JP-A-60-183030.
A granulation system 201 is further provided with a rotary vane 202a on the fluidization bed 107 and a driving motor 202 to rotate the rotary vane 202a below the bed 107. Heated air is supplied into the granulation tank 102 and the motor 202 is driven to rotate the vane 202a when the material A stored in the tank 102 is granulated. The material A directly receives rotating power of the vane 202a so that the material is prevented due to agitation from becoming porous.
According to the system 101 shown in FIG. 12, granulated material with a constant properties (particle diameter, particle shape, etc) is produced when material is granulated in a dilute fluidized layer by supplying a large amount of heated air into the granulation tank 102. However, in the prior art, the concentration of the material A in a fluidized layer is dense and the particles of the material A do not doesn""t have sufficient opportunity to touch each other so that particle growth becomes slow affecting the productivity of granulation.
Further, when a high density fluidized layer is formed in the granulation tank 102 by reducing the amount of the heated air supplied to the granulation tank 102, each particle of the material A comes collides frequently, so that the particle growth of particle becomes fast. However, the particle diameter of the granulated material doesn""t become uniform or projected parts like an antenna of a snail are formed on the surface of the particles so that granulated material with an irregular shape (not spherical) and different diameter is produced. Therefore, the system 101 can""t be used when spherical granulated material is required. Furthermore, as mentioned above, the granulated material tends to be porous because the granulation is executed in air. As the result, it is difficult to produce granulated material with small specific volume.
When heated air is supplied at a uniform rate into the granulation tank 102, the air may blow through a part of the material A placed on the fluidization bed 107. In this case some of the material A in the tank 102 remains still and isn""t fluidized. Granulated material isn""t made from such a material, therefore, and the amount of granulated material becomes less compared to the amount of raw material A.
Slacking, bubbling or chanelling of the material A, which stop fluidization, may be caused in the granulation tank 102 while the material is granulated. The particle diameter, particle shape, density, and hardness of the granulated material depend on the fluidized condition of the raw material A and the granulating material.
Further in the prior art, unintended fine particles may be included in the granulated material. It is desired to reduce the amount of such fine particles. When the system 201 shown in FIG. 13 is used, the granulated material is prevented from being porous because the rotary agitation flow by means of the rotation of the vane 202a. However, it is required to provide the rotary vane 202a on the fluidization bed 107 and the driving motor 202 below the bed 107 for rotating the vane 202a, whereby the number of the parts becomes large and the system is complicated. Foreign material may be produced from the increased parts and the complication makes the cleaning of the system difficult. Such foreign material remaining in the system may be included in the granulated material and increases the risk of contamination. Therefore, such a system isn""t appropriate for producing granulated material for fine chemical use such as medicine wherein a high quality granulation without contamination of foreign material is required.
The present invention is proposed to solve the above-mentioned problems. An object of the present invention is to provide a granulation method and system wherein granulated material with uniform shape, uniform diameter and uniform property and small specific volume can be easily and efficiently produced.
According to the granulation method of the present invention, powdered material stored in a granulation tank is produced into a granulated material with high density and small specific volume as follows.
The powdered material is fluidized by applying heated pulsating vibration air and is aggregated by spraying a binding solution. Therefore, the aggregated powdered material drops and is deposited on a fluidization bed by gravity accompanied by the growth of the particles while they are suspended up and down in the granulation tank according to the frequency of the pulsating vibration air. And thereafter the deposited powdered material under granulation is produced into a granulated material with high density and small specific volume while receiving compression to be high density by means of the heated pulsating vibration air.
According to such a production method, the deposited material under granulation is compressed to a high density by means of the vibration of the pulsating vibration air. Therefore, the projections like an antenna of a snail formed on the surface of the particles of the granulating material are peeled off and each particle of the granulating material deposited on the fluidized bed is compressed together. In the present invention, the produce of the granulated material with the projections or porous property is prevented and granulated material with uniform properties, high density and small specific volume is produced efficiently without difficulty comparing to the prior art wherein powdered material is fluidized by means of constant heated air mixed in the heated air, and a binding solution is sprayed to aggregate the material, and then the material is dried to grow as granulated material.
Four types of pulsating vibration air can be used in the present invention, that is, pulsating vibration air with peaks and valleys of negative pressure, air with peaks of atmospheric pressure and valleys of negative pressure, air with peaks of positive pressure and valleys of atmospheric pressure, and air with peaks and valleys of positive pressure. According to experimental findings, the granulated material with small specific volume and good quality can be obtained when pulsating vibration air with peaks and valleys of positive pressure is used.
It is preferable to use the pulsating vibration air with peaks and valleys of positive pressure.
In the specification xe2x80x9cpositive pressurexe2x80x9d means a condition that the pressure in the granulation tank is higher than the outside pressure (atmospheric pressure). xe2x80x9cNegative pressersxe2x80x9d means a condition that the pressure in the granulation tank is lower than the outside pressure (atmospheric pressure).
As the result of the actual production using different kinds of powdered material, the amplitude, frequency and wave shape of pulsating vibration air are desirable to be changed according to the property of the powdered material (such as viscosity, diameter, specific gravity, adhesiveness, and miscibility with air of the particles of the material) in order to produce granulated material with uniform properties and small specific volume.
At least either amplitude, frequency and wave shape of pulsating vibration air is changed according to the property of the material.
According to experimental findings, granulated material with small specific volume, that is heavy material, can be obtained when the frequency of the pulsating vibration air is not less than 1 Hz but less than 10 Hz, desirably from 1 Hz to 9 Hz, more desirably from 1 Hz to 6 Hz, still more desirably 5 Hz as the result of production with the pulsating vibration air with different frequency.
Therefore, its preferable to set the frequency of pulsating vibration air to not less than 1 Hz but less than 10 Hz in the production method of the present invention.
A granulation system, with air suction means provided for an air discharge port attached at the top of a granulation tank, with an air supply means provided for an air supply port at the bottom of a granulation tank, with both the air suction means and the air supply means may be considered. As a result of the production with these different granulation systems and a pulsating air generation means, when the pulsating vibration means is provided before the air supply port at the bottom of the granulation tank and pulsating vibration air is supplied under a fluidization bed and directed upwardly, it is easy to fluidize the raw material and suspend a part of the material up and down. Further, compression by means of the vibration of the pulsating vibration air is efficiently applied on the granulation and growing material which has been dropped and deposited on the fluidization layer and the material becomes dense, whereby granulated material with specific volume is produced.
The granulation system of the present invention is provided with a granulation tank for storing powdered material to be granulated. The granulation tank has a supply port for introducing heated air at the bottom thereof, a discharge port for discharging the introduced heated air at the top thereof, and a fluidization bed provided above the supply port for placing the powdered material temporarily. The granulation tank is also provided with spray means for spraying a binding solution to grow the powdered material to be granulated. The system is also provided with an air source connected to the supply port of the granulation tank via a conduit pipe, heating means interposed in the conduit pipe for heating the air generated from the air source, and a pulsating vibration air generation means interposed in the conduit pipe for converting the air generated from the air source to pulsating vibration air.
A pulsating vibration air generation means may be provided with an on-off valve for closing and opening a conduit pipe connecting the air source and the granulation tank so that pulsating vibration air is generated by operating the valve, may generate pulsating vibration air by vibrating a plate by means of the air supplied from an air source, or may be provided with an air suction means at an air discharge port at the top of a granulation tank and an on-off valve for opening and closing a conduit pipe connecting the air discharge port and the air suction means and pulsating vibration air is generated by operating the valve. According to the productive results using the above-mentioned different pulsating vibration air generation means, a rotary type pulsating vibration air generation means is desirable in order to produce granulated material with small specific volume, and more preferably, the rotary type pulsating vibration air generation means is preferably provided between the conduit pipe connecting the air source and the granulation tank.
The pulsating vibration air generation means as mentioned above may be provided with a casing having a pair of connecting ports at the surrounding wall thereof and a rotary valve having a rotational axis in the center of the casing. The valve is constructed so as to divide the inside of the casing into at least two spaces. One of the pair of connecting ports is connected with the heated air supply port and the other port is connected with the air source.
Some materials to be granulated are easy to be mixed with air and the others are not. Therefore, it may be preferable to change the wave shape of the pulsating vibration air in order to fluidize the material stored in the granulation tank and make some of the aggregated material suspend up and down according to the frequency of the pulsating vibration air.
According to the granulation system of the present invention, the above-mentioned pulsating vibration air generation means is provided with a valve for opening and closing the conduit pipe connecting the air source and the heated air supply port, and a valve cam mechanism having guide rails with a specific circular pattern defining the duration and amount of open and close of the valve. The valve is opened or closed vertically in compliance with the irregular pattern of the guide rails by driving the valve cam mechanism.